Tous les combattants
 | Orlando Wilson Prins | 2-4-0 REC | #3221 |  |
 | Ornella Vivaldi | 0-1-0 REC | #7917 |  |
 | Oron Kahlon | 0-1-0 REC | #5601 |  |
 | Ortsa Gudaev | 1-1-0 REC | #5129 |  |
 | Osama Elsaidy | 0-1-0 REC | #7187 |  |
 | Oscar Jurado Sanchez | 1-0-0 REC | #1251 |  |
 | Oscar Mendez | 0-1-0 REC | #5120 |  |
 | Oscar Miguel | #7806 |  | |
 | Oscar Ownsworth | 2-3-0 REC | #499 |  |
 | Oscar Ravello | #8056 | | |
| Oseas Cruz Furtado | 0-1-0 REC | #7868 |  |
 | Oseyiomon Oiyemhonlan | 1-2-0 REC | #4696 | |
 | Osimkhon Rakhmonov | 2-1-0 REC | #2452 |  |
 | Oskar Piechota | 2-3-0, 1NC UFC | #3759 |  |
 | Oskar Stachura | 0-1-0 REC | #5083 | |
 | Oskar Staszczak | 1-0-0 REC | #2364 | |
 | Oskar Szczepaniak | 4-2-0 REC | #2964 | |
 | Osman Minbatirov | 1-1-0 REC | #5886 | |
 | Osvaldo Benedito | 0-1-0 REC | #5244 |  |
 | Otabek Rajabov | 1-0-0 REC | #3454 | |
 | Otar Tanzilov | 0-1-0 REC | #4848 |  |
 | Otari Tanzilovi | 0-1-0 UFC | #4301 | |
 | Otgonbaatar Boldbaatar | 0-1-0 REC | #5671 |  |
 | Oton Jasse | 0-3-0 REC | #4256 | |
 | Ottman Azaitar | 2-3-0 UFC | #1879 |  |